Polyester films have excellent heat resistance, mechanical properties, chemical resistance, etc., and therefore, are widely used as base films for audio and video recording media. Recently, magnetic recording is rapidly shifting to high density recording and perpendicular magnetic recording has come to be employed. Among the magnetic materials for perpendicular magnetic recording, barium ferrite is attracting attention because of its high density recording characteristics as well as its stability and productivity. For instance, when a digital audio tape (DAT) is duplicated at high speed by contact magnetic transfer method, the duplicated tape must be capable of high density recording of a 0.67 .mu.m wavelength at low coersive force as low as 700 Oe. Magnetic recording tapes using barium ferrite as a magnetic material, which satisfy the above requirements, have now come into practical use.
However, it has been found that magnetic recording media using barium ferrite are inferior in durability to those using .gamma.-ferrite or metal. More specifically, magnetic recording tapes using barium ferrite are susceptible to deformation at edge portions when used over long periods of time.
Also magnetic recording media using barium ferrite are inferior in light-shielding property to those using .gamma.-ferrite or metal. Floppy discs and magnetic tapes are usually positioned properly by detection of an optical positioning hole or tape leader. Therefore, various attempts have been made for providing barium ferrite magnetic media with sufficient light shielding property.